1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, a process cartridge that includes an electrophotographic photosensitive member, and an electrophotographic apparatus.
2. Description of the Related Art
Presently, the mainstream electrophotographic photosensitive member used in process cartridges and electrophotographic apparatuses are those that contain organic photoconductive substances. An electrophotographic photosensitive member typically includes a support and a photosensitive layer formed on the support.
An undercoat layer is often interposed between the support and the photosensitive layer to suppress charge injection from the support side toward the photosensitive layer side and to suppress occurrence of image defects such as black dots.
In recent years, electrophotographic photosensitive members have come to contain charge generating substances having high sensitivity. However, as the sensitivity of the charge generating substances increases, the amount of charges generated is increased and charges tend to remain in the photosensitive layers, resulting in a problem called ghosting. In particular, a phenomenon called positive ghosting in which only the density of the portion irradiated with light during the previous rotation is increased in an output image is likely to occur.
Such a ghosting phenomenon has been suppressed by, for example, adding an electron transporting substance to the undercoat layer. From the viewpoint of flexibility of the material design of a photosensitive layer on the undercoat layer, an undercoat layer containing an electron transporting substance desirably uses a curable material that is sparingly soluble in solvents contained in coating solutions for forming photosensitive layers. PCT Japanese Translation Patent Publication No. 2009-505156 discloses an undercoat layer that contains a polymer obtained from a crosslinking agent and a condensation polymer (electron transporting substance) that has an aromatic tetracarbonylbisimide skeleton and a crosslinking portion. Japanese Patent Laid-Open No. 2006-178504 discloses an undercoat layer containing a polymer of an electron transporting substance that has a non-hydrolyzable condensation-polymerizable functional group.
In recent years, the quality requirements for the electrophotographic images have become more and more stringent and the permissible range for the positive ghosting has also narrowed.
The inventors of the present invention have conducted extensive studies and found that the techniques disclosed in PCT Japanese Translation Patent Publication No. 2009-505156 and Japanese Patent Laid-Open No. 2006-178504 have room for improvements as to suppression of positive ghosting. In addition, when charges tend to remain in the undercoat layer and at the interface between the undercoat layer and the photosensitive layer, the potential easily fluctuates after repeated use. Thus, the potential fluctuation needs to be decreased.